Magnetron



De.1o,19.46. 'G L, USSELMAN 2,412,372

MAGNETRON Filed Oct. 26, 1943 mvENToR svg ATTORNEY Patented Dec. 10, 1946' y MAGNETRON 'y George L. Usselxnan, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporationof Delaware Application october 26, 1943, serial No. 507,697

This invention relates generally .to ultra high frequency magnetron oscillation generators, and particularly to magnetrons of the type having an anode so constructed that it forms a circuit resonant to the frequencyA at which the device is intended to operate. s

For the purpose of generating ultra high frequency oscillations modulated in amplitude, it is known to employ a magnetron having an anode provided on its inner surface with a plurality of substantially cylindrical grooves or cavities disposed parallel to and symmetrical with the cathode. The grooves or cavities form tubes having inductances dependent upon the dimensions thereof, and the portions of the anode between the grooves form capacitances with each other and with the cathode, the capacitances valso being dependent upon the dimensions of these portions and the spacing thereof relative to each other and to the cathode. The anode of this type of magnetron can be said to be composed of a plurality of inwardlyv projecting anode portions. These anode portions may comprise an even number and be substantially or effectively spaced from one another by one-half wavelength at the operating frequency of oscillations. Reference is herein made to Hansell United' States Patent #2,217,745, granted October 15, 1940, and to Samuel United States Patent #2,063,342, December 8, 1936, for this known type of magnetron.

The present invention, broadly stated, is a modification of the foregoing type of magnetron which makes it possible to obtain frequency modulated oscillations in a novel and eflicient manner.

' A more detailed description of the invention follows in'conjunction with a drawing wherein:

Figure 1 shows substantially a half sectional view, partly in perspective, of a magnetron in accordance with the present invention, in a circuit for producing frequency modulated oscillations; and I Figure 2 shows a plan view of the magnetron of Figure 1 with the pole face removed to show the configuration of the anode groves more completely.

The magnetron of the invention isshown as having an anode A provided with eight grooves or cavities, although it should be understood that any other desired number of grooves can be employed. The upper end of these cavities are designated e, while the lower ends are designated e'.

The lips of the cavities which define the boundaries of the inwardly protruding anode portions 16 Claims. (Cl. 179-1715) `upon which the electrons impinge are designated L. The cathode is K and extends linearly along the central axis of the magnetron or central chamber. Split disc-like rings GI and G2 are shown around each` end of the cathode K and 1ocated at each end ofthe magnetron central chamber. The envelope of the magnetron, which is evacuated, is not shown in order to simplify the drawing.

An important feature of the magnetron of the invention lies in the novel construction of the groovesor cavities by reason of which the lip circle or inner walls of the central chamber tapers outwardly in going from lthe top to the bottom, and the diameters vof the grooves grow larger from end e to end e, as shown. The order of the change in dimensions may be reversed without aecting the principles of the invention.

A eld magnet with poles N and S (north and' south) produces a magnetic iield parallel to the cathode to influence the movement of the electrons emanating from the cathode. If desired,

this magnet may be replaced by a iield coil surrounding the anode and producing an intense but constant magnetic field which has flux lines running parallel4 through the envelope in a dif `rection parallel to the cathode.

The disc-like rings GI and G2 may be referred to as grids or control electrodes and are shown connected to opposite ends of the secondary winding S of an audio frequency transformer T to whose primary Winding P is applied the audio modulating signal in the form of speech or Aoscillations. anode A by condensers B. The midpoint ofthe secondary winding S is connected to a source of negative bias potential. The anode A is grounded at GRD, while high negative direct current potential and 10W voltage heater current are supplied to the cathode K through leads J and H,

respectively. It will thus be seen that the anode A is at a high direct current positive potential relative to the cathode K. An output or pick` up loop D is located in one of the grooves or cavities for abstracting ultra high frequency oscillations. This loop connects to a suitable output circuit such as a transmission line or antenna by means of leads F. The principles of operation of the magnetro and its circuit will now be described. In general, when free electrons are liberated from the cathode K by the action ofy heat, they are pulled toward the anode by its positive potential. Now it is known that when an electron moves perpendicularly across a magnetic field it will describe a The ring grids are by-passed to" the" r vof the electron.

l v I 3 concentric or curved path in the magnetic field.

strength and .anode voltage are made, the electrons will curve into the magnetron inner walls and start feeble oscillations in the cavities. Once oscillations have started, alternate positive and negative potentials appear on the lips L of the cavities. The electrons, in passing these alternately charged cavity lips in their curved orbits, become hunched in groups. By proper adjustments of field strength and anode potential, these bunches of electrons are caused to fall at reduced velocity on the negatively charged lips of the cavities. 'I'his increases the efllciency of the magnetron and causes the oscillations in the cavities to grow stronger so thatv comparatively large amounts of ultra high frequency power may be obtained from this type of magnetron.

vof the magnetron of Figures 1 and 2 are entirely illustrative and not definitive.' It should be understood that the theoretical explanation given above is for the purpose of exposition in order that the inventionmay be better appreciated. While this explanation is believed to be correct, it is notl of necessity complete. nor does the operation of the invention depend upon its accuracy or otherwise.

What is claimed is: l. An electron discharge device comprising cathode electrode and an anode electrode cooperatively disposed with respect to said cathode, said anode having an electron receiving portion in proximity to said cathode and a grooved portion spaced from said first portion forming an inductance which together with the capacitances between said electrodes constitutes an electrical circuit, said grooved portion tapering from. one end to the other.

2. An electron discharge device comprising a cathode. and an anode having electron receiving The electrons from the cathode ,K are caused to move toward the anode in either the larger or the smaller end of the magnetron by the differences of negative bias potentials on ring grids other words, if ring grid Gi is more' negative than -Gi and G2 produced by the applied signals. In

grid G2. the electrons will be forced to occupy, or

be repelled to. the smaller dimensioned portions of the magnetron, as a result of which the frequency of the magnetron oscillations will be increased. Again,'if in the audio signal cycle the grid G2 is biased more negative than grid GI, then the electrons, willbe forced to occupy the portion of the magnetron chamber having larger dimensions as a consequence of which the frequency of themagnetron will be decreased. This followsbecause with proper design, changes in dimensions of a magnetron changes its operating frequency. due to changes in the orbital paths taken by the electrons. Of course, this ordinarily requires changes 4in magnetic field density and cathode-to-anode potential. Howevena certain amount of frequency variation can be obtained by causing the electrons to oscillate in various regions of the magnetron having different dimensions but with fixed magnetic field and fixed electric potentials. Because of the fact that the Q of a circuit becomes lower as the operating frequency becomes higher, it is possible to obtain more frequency deviation at these high frequencies than that usually obtained at the lower frequencies. In other words, a high frequency circuit can be frequency modulated over a wider band when compared to that obtained in low frequency oscillators, although the perlcentage of frequency variation might be the same in both cases. The ileld strength and electric potentials serve as limiting factors controlling `the amount of frequency deviation obtainable from the magnetron of this invention.

l The ring grids GI and G2 are shown split in one place in order to eliminate the possibility of magnetic effect on them. Grids GI and G2 are by-passed with condensers B to prevent the radio frequency from aifecting the modulating circuits.

Insulation and mounting means are not shown since they do not ail'ect the principle of operation which the invention describes. 'I'he cooling fins usually fastened to the anode are omitted here for simplicity. Only such parts of the magnetron considered necessary for the description of the invention are shown.

It should be understood that the dimensions surfaces disposed about said cathode. said anode having also a plurality of longitudinal groov in its inner walls disposed remote from, and symmetrical with said cathode, said grooves being smaller at one end than at the other. A

3. An electron discharge device comprising an anode having arms bounding a cavity and forming an inductance, said arms and said cavity tapering from one end to the other.

4. An electron discharge device comprising a cathode and a continuous anode surrounding said cathode, said anode having an even number of regularly spaced portions bent inwardly toward said cathode and terminating in juxtaposed surfaces, thereby substantially enclosing a plurality of cavities, said cavities each having an opening which tapers from one end to a larger opening at the other end, and means for producing a magnetic ileld with flux lines running parallel to said cathode. f

5. A magnetron oscillator comprising an electron discharge device having an enclosing vessel containing an electrode having arms bounding a cavity and forming an inductance, said arms terminating. in juxtaposed substantially parallel lines, said cavity having an opening which tapers from one end to an opening of different dimensions at the other end.

6. An oscillation generator comprising an electron discharge device having a cathode and a continuous anode surrounding said cathode, said anode consisting of an even number of regularly spaced portions bent inwardly toward said cathode and terminating in juxtaposed surfaces to thereby form an even number of similarly arof said cathode and located between said cathode and the adjacent surfaces of said anode.

8. An electron discharge device comprising a cathode and a continuous anode surrounding said cathode, said anode having an even number of regularly spaced portions bent inwardly toward said cathode and terminating in juxtaposed surfaces to thereby substantially enclosing a plurality of cavities, said anode spaced portions surrounding a central chamber along whose axis the cathode is located, said chamber tapering from one end to the other, and a pair of disc-like control electrodes at opposite ends of said chamber substantially surrounding said cathode.

9. An electron discharge device comprising-a cathode and a continuous anodesurrounding said cathode, said anode having an even number of regularly spaced portions bent inwardly toward said cathode thereby enclosing a central chamber along whose axis the cathode is located, ad-

jacent anode spaced portions also formingv grooves with one another winch form inductances, said central chamber and saidl grooves tapering in the same direction from one end to the other, a pair of disc-like control electrodes arranged in different planes and located at opposite ends of said chamber, said control electrodes substantiallyv surrounding said cathode in said planes. l

10. An'electron discharge device comprising a cathode and a continuous anode surrounding said cathode, said anode having an even number,of regularly spaced portions bent inwardly toward said cathode thereby enclosing a central chamber` along whose axis the -cathode is located, adjacent 'anode spaced portions also forming grooves with one another which form inductances, said central chamber and said grooves tapering in the same direction from one end to the other, a pair of control electrodes arranged in different planes and located at opposite ends of said chamber, said control electrodes substantially surrounding said cathode in said planes, and means for producing a magnetic field with flux lines running parallel to said cathode. i

11. An oscillation generator system compris-- ingk an electrondischarge device having a cathode and a continuous anode surrounding said cathode, said anode having a number of. regularly spaced portions bent inwardly toward said cathode thereby enclosing a central chamber along whose axis the cathode is located, adjacent anode spaced portions also forming grooves with one another which form inductances, said central chamber and said grooves tapering in the same direction from one end to the other, a pair of control electrodes arranged in different planes and located at opposite ends of said chamber, said control electrodes `substantially surrounding said cathode in said planes, means for producing a magnetic field having flux lines running parallel to said cathode,and means coupled to both of said control electrodes for modulating the oscillations produced by said electron discharge device.

12. An oscillation generator system comprising an electron discharge device having 1a cathode and a continuous anode surrounding said cathode,rsaid anode having a number of regularly spaced portions bent inwardly toward said cathode thereby enclosing a, central chamber along whose axis the cathode is located, adjacent anode spaced portions also forming grooves with one another which form inductances, said central chamber and said grooves tapering' in the same direction from one end to the other, apair of control electrodes arranged in different planes and located at opposite ends said control electrodes substantially surroundof said, chamber,

ing said cathode in said planes, means for producing a magnetic eld having flux lines running parallel to said cathode, and means coupled vto both of said control electrodes for modulating the oscillations produced by said electron discharge device, said last means including an audio frequency transformer having a primary winding coupled to a source of modulating potentials'and a secondary winding each of whose terminals is y portions also forming grooves with one another Which form inductances, said ycentral chamber and said grooves tapering in the same' direction from one end to the other, a pair of control electrodes arranged in different planes and located at opposite ends of said chamber, said control electrodes substantiallysurrounding said cathode in said planes, means for producing a magnetic field having flux lines running parallel to said cathode, means for supplying a bias to said control electrodes which is negative relative to said cathode, and means for changing the relative bias of said two control electrodes in accordance with changesl in modulation potential to thereby changethe frequency of the oscillations produced by said oscillator, and a load circuit coupled to one of said grooves for deriving frequency modulated oscillations. y

14. An electron discharge device comprising an anode having arms bounding a cavity and formingan inductance, said arms and said cavity tapering from one end to the other, a cathode for said device, and a pair of control electrodes at opposite ends of said cathode and located between said cathode and .the adjacent surfaces of said anode.

15. An electron discharge device comprising an anode having arms bounding a cavity and forming an inductance, said arms and said cavity tapering from vone end to the other, a cathode for said device, and a.y pair of `control electrodes at opposite ends of said cathode an-d located between said cathode and the adjacent surfaces of said anode, means for supplying a bias to said control electrodes which is negative relative-to said cathode, and a. circuit for changing the bias of said pair of control electrodes relative to each other in accordance with changes in modula-v parallel to said cathode, said anode having grooved portions substantially symmetricallydisposed with respect to said cathode and constitutlng inductances and having other portions constituting capacitances with each other and with said cathode, said grooved and other portions forming a tuned circuit, said grooved portions having di'erent dimensions at different points in their lengths.

` GEORGE L. USSELMAN. 

